Control circuit for inductive loads

Abstract

A control circuit for controlling the current through an inductive load powered by a unipolar power source. The current through the inductive load is controlled by three electronic switches and a subcircuit. The switches provide three different voltage levels across the inductive load. The closing of the first switch supplies positive voltage across the load, thereby increasing the load current. Opening of the first switch and closing of the third switch disconnects the power source from the load and short circuits the inductive load resulting in zero voltage across the load. Opening of the third and first switches directs the inductive current through the subcircuit, developing a negative voltage across the load and thereby rapidly decreasing the inductive current. By controlling the load voltage between a positive and zero voltage and between a negative and zero voltage, the load current is changed quickly and efficiently.

What is claimed is: 
     
       1. A control circuit for controlling current flow through an inductive load powered by a unipolar power source, comprising: first, second and third electronic switches connected in sequential series between positive and negative terminals of said power source and said second and third switches connected in series between positive and negative terminals of said load;   the first switch being connected to allow or block positive voltage therethrough, the second switch being connected to block positive voltage and allow negative voltage therethrough, and the third switch connected to allow or block negative therethrough;   said third switch being connected in a subcircuit to develop a negative voltage drop across the load during a discharge condition; and   a drive circuit for closing of the said first switch to connect positive voltage from the power source across the load causing an increasing load current, opening of the first switch and closing the third switch to disconnect the power source from the load and short circuit the inductive current, and opening of the third and first switches to direct decaying inductive current through the subcircuit causing a negative voltage across the load, the subcircuit and the third switch together providing a path for current flow resulting in rapid decay of the inductive current;   wherein said subcircuit includes a zener diode and a diode connected in series between a gate and a drain of the third switch whereby upon opening of the first and third switches, said third switch is closed by the negative voltage across the subcircuit of the zener diode and the diode and said subcircuit provides a path for rapid decay of the inductive current flow.   
     
     
       2. The control circuit of claim 1 wherein the second switch is a schottky diode. 
     
     
       3. The control circuit of claim 1 wherein the second switch is a MOSFET transistor connected with said subcircuit.